There has been conventionally known a classifying apparatus that uses guide vanes or air nozzles to generate a whirling gas stream in a classifying chamber to impart a whirling motion to powder supplied into the classifying chamber for separating the powder into fine powder and coarse powder by a centrifugal force, the fine powder being collected from the central part of the whirling gas stream and the coarse powder being collected from a lower peripheral portion of the whirling gas stream.
Aside from that, in recent years, with the advancement in technology of electronic components and the like such as a capacitor, there is demand for fine particles having a narrow particle size distribution.
To cope with it, for instance, in Patent Literature 1, the applicant proposes a powder classifying apparatus in which a disc-like cavity serving as a classifying site for centrifuging powder having a particle size distribution is formed between two disc-like members; a plurality of guide vanes are arranged at an outer periphery of the disc-like cavity so as to extend from the outer periphery of the disc-like cavity toward an inner direction at a predetermined angle; a powder supply port for supplying the powder to the disc-like cavity is disposed at an upper disc-like member; a discharge unit for air streams including fine powder discharged from the central part of the disc-like cavity is disposed in the central part of the upper disc-like member; a collection unit for coarse powder discharged from the disc-like cavity is disposed between a lower portion of an outer edge portion of a lower disc-like member and an outer peripheral wall of the disc-like cavity; a plurality of first air nozzles for blowing compressed air into an inside of the disc-like cavity are arranged near the powder supply port and above the plurality of guide vanes on the outer peripheral wall of the disc-like cavity so as to extend along tangential directions of the wall; and a plurality of second air nozzles for blowing compressed air into an inside of the disc-like cavity are arranged at the collection unit of coarse powder and below the plurality of guide vanes on the outer peripheral wall of the disc-like cavity so as to extend along tangential directions of the wall.
With this configuration, the powder classifying apparatus disclosed in Patent Literature 1 sucks and discharges air through the discharge unit by use of a blower to cause air sucked from the outside of the apparatus to pass through the guide vanes to thereby form a whirling gas stream in the disc-like cavity which serves as a centrifuge chamber (classifying site), thus imparting a whirling motion to the powder and separating the powder into coarse powder and fine powder by a centrifugal force. At this time, the apparatus blows compressed air into the inside of the disc-like cavity through the first air nozzles to cause the powder supplied from the powder supply port to join the whirling gas stream and blows compressed air to the lower portion of the outer edge portion of the disc-like cavity through the second air nozzles to return, to the disc-like cavity, fine powder mixed in coarse powder to be collected through a coarse powder collection port, thereby accurately sorting out fine powder of up to about several micrometers or submicron size.
As a result, in Patent Literature 1, the powder classifying apparatus is attained which can accurately sort out (classify) fine powder of up to about several micrometers or submicron size, enables easy control of the particle size, and allows easy maintenance.
Besides, for instance, in Patent Literature 2, the applicant proposes a powder classifying apparatus in which formed in a casing are a disc-like centrifuge chamber for centrifuging powder having a particle size distribution, and a ring-shaped powder dispersion chamber and a ring-shaped powder reclassifying chamber which are located separately at the opposite sides of the centrifuge chamber to be coaxial therewith and to communicate with the centrifuge chamber; the outer peripheral portion of the centrifuge chamber is closed by a peripheral wall; formed at the casing are a powder supply port for supplying powder into the powder dispersion chamber, a fine powder discharge port for discharging air stream including fine powder from the centrifuge chamber, and a coarse powder discharge port for discharging coarse powder from the powder reclassifying chamber; a plurality of first air nozzles for ejecting compressed air into the inside of the powder dispersion chamber and a plurality of second air nozzles for ejecting compressed air into the inside of the powder reclassifying chamber are arranged on the peripheral wall of the casing along a circumferential direction thereof to generate a first whirling gas stream for dispersing the powder in the powder dispersion chamber and a second whirling gas stream for allowing fine powder mixed in coarse powder in the powder reclassifying chamber to float and return to the centrifuge chamber; and a third whirling gas stream is generated using the above two whirling gas streams for classifying (centrifuging) the powder having a particle size distribution in the centrifuge chamber.
With this configuration, the powder classifying apparatus disclosed in Patent Literature 2 generates the first whirling gas stream in the ring-shaped powder dispersion chamber by use of compressed air ejected from the first air nozzles to the powder dispersion chamber to allow the powder supplied through the powder supply port to be carried and dispersed by the first whirling gas stream while causing the powder to enter a disc-like cavity which serves as the centrifuge chamber and communicates with the powder dispersion chamber, and generates the second whirling gas stream in the ring-shaped powder reclassifying chamber by use of compressed air ejected from the second air nozzles to the powder reclassifying chamber to allow fine powder mixed in coarse powder to float and return to the centrifuge chamber while causing the floating fine powder to enter the disc-like cavity which serves as the centrifuge chamber and communicates with the powder reclassifying chamber, whereby the third whirling gas stream for classifying the powder is generated in the disc-like cavity to impart a whirling motion to the powder and separate the powder into coarse powder and fine powder by a centrifugal force, thereby accurately sorting out fine powder of up to about several micrometers or submicron size.
As a result, Patent Literature 2 enables fine particles to be accurately sorted out.    Patent Literature 1: JP 2009-34560 A    Patent Literature 2: JP 2011-45819 A